1. Field of the Invention
The invention relates to closures for containers.
In this specification, a so-called "child-resistant" closure (hereinafter referred to as a "relevant child-resistant closure") comprises an inner closure part adapted to be engaged with the neck of a container by rotation in one sense and to be disengaged therefrom by rotation in the other sense; an outer closure part capable of being moved relative to the inner closure part between a predetermined rest position and a displaced position; means to rotate the inner closure part with the outer closure part on rotation of the latter in the one sense when the outer closure part is in either of its rest position and its displaced position; and means to rotate the inner closure part with the outer closure part on rotation of the latter in the other sense when the outer closure part is in its displaced position, but when the outer closure part is in its rest position only when any torque resisting rotation of the inner closure part is below a predetermined threshold; wherein the outer closure part is capable of adopting its displaced position only when its angular displacement with respect to the inner closure part is within any one of a number of predetermined discrete angular ranges. It will be appreciated that the term "discrete angular ranges" covers the case where the ranges are zero, and the outer closure part can adopt its displaced position only at discrete angles relative to the inner closure part.
The closure according to the invention is particularly suitable for use in the arrangement described in U.S. patent application Ser. No. 706,891 (now U.S. Pat. No. 5,213,225) and/or that described in U.S. patent application Ser. No. 769,198, filed 30th Sep., 1991 corresponding to U.K. Patent Applciation No. 9114871.8, the disclosures of which applications are included herein by way of reference.
2. Description of the Prior Art
Many known child-resistant closures include a plurality of equidistant ramps on the outer surface of a crown portion of the inner closure part which cooperate with a plurality of equidistant, resilient oblique blades extending inwardly from a crown portion of the outer closure part. When viewed from the center of the respective closure parts, the ramps have a right triangular section comprising a horizontal base, a vertical left side and a hypotenuse and the blades extend diagonally downward from the left towards a lower right free end.
When the outer closure part is rotated clockwise, i.e. in a right-handed sense, the free ends of the blades abut the vertical faces of the ramps, thereby driving the inner closure part with the outer closure part.
When rotation of the outer closure part is effected in the other, left-handed sense, i.e. counterclockwise, the blades simply trail over the ramps in the manner of a ratchet, the inner closure part being fixed on the container by its closure torque.
Typically, castellations are provided on both inner and outer closure parts which mate when the outer closure part is depressed. The inner closure part is then bound to rotate with the outer closure part. When the outer closure part is released, the blades act as leaf springs to return it to its rest position, in which the castellations are disengaged.
Child-resistant closure systems normally rely on the ability of the closure to spring apart, every time, after pressure has been applied, generally at right angles to the plane of the thread. If, even on rare occasions the two parts of the closure do not spring apart and disengage, the child-resistant feature of the closure no longer functions. It is therefore essential that the blades acting as leaf springs have and continue to retain sufficient resilience to exert sufficient pressure to force the two parts of the closure apart in order that there is disengagement at all times, apart from occasions when direct and sufficient pressure is applied to engage the closure system. The main failure of existing systems to work properly at all times is due to the weakness of the leaf springs which in the past have typically been made of uniform thickness, with a sharp angle on the inside edge where the leaf spring joins the flat face of the underside of the top part of the closure. This design is potentially unsatisfactory as the leaf springs can weaken at the point of joining the flat plane of the underside of the top part of the closure, and the leaves themselves tend to be stiff and as a result do not flex along the length of the spring leaf. To overcome this problem and to ensure more flexibility and to ensure that the leaf springs retain their resilience and hence the ability to force the two parts of the closure apart, and also to ensure that when being closed the planes of the top and lower part of the closure remain in parallel planes, the invention provides a relevant child-resistant closure comprising a plurality of cantilever leaf springs extending obliquely from one part of the closure towards the other part of the closure, each cantilever leaf spring having a cross-section which tapers towards its free end, and the profile at the acute angle between each cantilever leaf spring and the closure part from which said spring extends is radiused.
Another problem arises where a closure is primarily intended for use by the elderly, and hence must be easy to open, but which, for safety, must be child-resistant. The number of castellations provided on known child-resistant closures is normally two, three or four, but this can require the closure to be rotated for up to 180.degree. before engagement of the castellations can take place. Engagement after a much smaller rotation is desirable, and according to a further aspect of the invention there is provided a container neck and closure therefor wherein the closure moves from fully closed to a fully open position by relative rotation through less than 360.degree., preferably approximately 90.degree. or less, the closure being a relevant child-resistant closure and the number of predetermined discrete angular ranges being such that angular displacement of the outer closure member relative to the inner closure member between adjacent positions in which the outer closure member can move to its displaced position is not greater than 45.degree., and preferably not greater than 25.degree.. A preferred angular displacement is 22.5.degree., in which case, from a normal rest position, the outer closure would move to a position where it could be moved with its displaced position by rotation through 12.25.degree. relative to the inner closure member. This preferred arrangement is provided by the closure having sixteen castellations, in which the maximum turn required for engagement is only one sixteenth, i.e. 22.5.degree.. This is an important feature when used in conjunction with the container and closure of U.S. patent application Ser. No. 706,891, where, in the preferred embodiment, the closure can be removed in only a quarter turn, and the addition of the child-resistant feature does not reduce the capacity to open the closure in approximately a quarter turn. This aspect particularly assists and supports ease of opening for the elderly and frail with only a twist of the wrists, without the necessity to let go of the closure of the container, even though being child-resistant.
The number of ramps in known closures varies, but is commonly three, four or six. The number of blades should be greater than two for stability, and should be a factor of the number of ramps.
In the past it has been arranged that the discrete angular ranges of angular displacement of the closure parts at which the castellations may engage one another is one in which the free ends of the blades on the outer closure part lie between ramps on the inner closure part.
A result of this is that it is perfectly possible for a container on which such a closure is installed to be left with the closure parts so oriented that the castellations may be engaged simply by immediate depression of the outer closure part. Such a situation can occur where a closure has been installed with the outer closure part depressed, or where an adult has depressed the outer closure part, but then changed his mind about removing the closure.